It sounds like something you might pitch to a Hollywood studio. A high-security US radiation lab is thrown into turmoil when a cylinder spewing out deadly radiation gets trapped in its network of delivery tubes. A robot is sent to try and free the canister before the radiation eats away at its circuits. After a string of failures, the intrepid machine saves the day.

The drama happened in October, at the US defence department's White Sands Missile Range in New Mexico. Records released this week describe how the base's Gamma Irradiation Facility was paralysed when a cylinder containing cobalt-60 became lodged in one of the lab's air-pressure tubes, similar to the document-delivery systems once used in offices.

The cobalt, powerful enough to kill a person in half a minute, got jammed between its storage area and the site where it was to be used to test the effects of radiation on vehicles and circuit boards. Once stuck, there was no way that lab staff could go near the tube, even wearing radiation suits. They watched from their control room as the lab's radiation alarms began to blare.

After trying to dislodge the canister by upping the pressure in the tube, the team called in a 270-kilogram bomb-disposal robot from the nearby Sandia National Laboratories. The remote-controlled machine, bristling with drills and robotic arms, seemed perfect for the job. But the radiation would disable its circuits within 50 minutes, its handlers calculated.

Race against time

The canister, about the size of a salt cellar, was jammed against a seesaw-shaped switch inside the tube that was stuck in the wrong orientation. So the robot drilled a hole in the tube to try and wiggle the switch back into position.

Two attempts failed. The robot then tried drilling straight into the switch's hinge, to allow the whole thing to be pushed aside. But the high pressure used to try and blow the canister out had buckled the switch out of shape.

By now, the robot had been in the radiation zone for 90 minutes. The team decided to regroup, but the robot's electronics had failed and it was rooted to the spot. Thankfully, the team had tied a rope around the machine, and it was hauled in, almost knocking over a radiation shield in the process.

Try, try again

The team sent the robot back the next day, determined to unscrew a section of the tube's metal panelling and remove the switch. They fitted a plastic part to the robot that would allow its screwdriver to engage with the screws. But the radiation melted the plastic.

On the third day, and after three weeks of continuous warning sirens, the team sent in the robot with a metal screwdriver. It unscrewed the plate, dislodged the switch, and sent the tube safely to its storage bay.

"The team effort produced a marvellous job," says White Sands staff member Richard Williams. It is unclear whether, once their headaches have gone and their well-chewed fingernails have grown back, the team will sell the movie rights to their escapade. The robot, nicknamed Mighty Mouse or M2 for its heroics, is taking a well-earned rest.